As an optical disc apparatus adapted for reproducing moving picture data or speech data recorded on a recording medium such as an optical disc, etc. by a picture compressing method in conformity with a predetermined standard, e.g., MPEG (Moving Picture Experts Group), etc., there is, e.g., an apparatus disclosed in the specification and drawings of EUROPEAN PATENT APPLICATION publication number: 0 522 853 A2 (Date of publication of application 13 January 1993. Bulletin 93/02) which has already field by the applicant of this application.
Namely, as shown in FIG. 1, in this optical disc apparatus, pick-up 2 irradiates laser beams onto optical disc 1 to reproduce, e.g., picture data recorded on optical disc 1 from its reflected light. Data that pick-up 2 outputs is inputted to demodulating circuit 3, at which it is demodulated. Moreover, output of pick-up 2 is inputted also to PLL (Phase Locked Loop) circuit 9. Thus, clock is extracted. This clock is sent to demodulating circuit 3 and sector detecting circuit 4. The data demodulated by the demodulating circuit 3 is inputted to error processing (ECC: Error Check and Correction) circuit 6 through sector detecting circuit 4.
In this example, sector detecting circuit 4 detects sector No., i.e., address allocated to sector of optical disc 1 from data demodulated at demodulating circuit 3 to output it to control circuit 31. Moreover, the sector detecting circuit 4 is operative so that when it fails to detect, e.g., sector No., or when even if it can detect those numbers e.g., are not continuous, it outputs sector No. abnormal condition signal to track jump judging circuit 7.
ECC circuit 6 detects data error from data delivered from demodulating circuit 3 through sector detecting circuit 4 to carry out error correction by using parity bit added to that data. Further, ECC circuit 6 is operative so that when it fails to correct error of data, it outputs error generation signal to track jump judging circuit 7. The error corrected data is delivered from ECC circuit 6 to ring buffer memory 5 for track jump, and is stored thereinto in accordance with control by control circuit
The control circuit 31 reads addresses every respective sectors of optical disc 1 from output of sector detecting circuit 4 to designate write address, i.e., write point (WP) for storing data from ECC circuit 6 into ring buffer memory 5 in correspondence with that address. Moreover, the control circuit 31 designates read-out address, i.e., reproduction point (RP) of data written in ring buffer memory 5 on the basis of code request signal from video code buffer memory 10 of decode section 20 of the succeeding stage. Then, the control circuit 31 reads out data from the reproduction point (RP) to deliver the data thus read out into video code buffer memory 10 to store it thereinto.
Data stored in the video code buffer memory 10 is transferred to inverse VLC circuit 11 on the basis of code request signal from inverse VLC (Variable Length Coding) circuit 11 of the stage succeeding thereto. The inverse VLC circuit 11 allows data inputted thereto to undergo inverse VLC processing, whereby when inverse VLC processing of the inputted data is completed, it outputs that data to inverse quantizing circuit 12, and outputs code request signal to video code buffer 10 to make a request for input of new data. Further, the inverse VLC circuit 11 respectively outputs quantization step size and motion vector to inverse quantizing circuit 12 and motion compensating circuit 15.
The inverse quantizing circuit 12 inverse-quantizes inputted data in accordance with quantization step size delivered from the inverse VLC circuit 11 to output it to inverse DCT circuit 13. This inverse DCT (Discrete Cosine Transform) circuit 13 allows inputted data to undergo inverse DCT processing to deliver it to adding circuit 14.
In the case where data delivered from inverse DCT circuit 13 to adding circuit 14 is data of I picture, that data is outputted to frame memory 16 as it is through adding circuit 14, and is stored thereinto.
Moreover, in the case where corresponding data is data of P picture in which I picture in the MPEG system is used as predictive picture, already decoded data of I picture is read out from frame memory 16, and is delivered to motion compensating circuit 15. This motion compensating circuit 15 implements motion compensation corresponding to motion vector delivered from inverse VLC circuit 11 to the data delivered from frame memory 16 so that predictive picture is provided to deliver it to adding circuit 14. The adding circuit 14 adds data outputted from inverse DCT circuit 13 and data outputted from motion compensating circuit 15 to generate data of P picture. This data is also stored into memory 16.
In the case where data outputted from inverse DCT circuit 13 is data of B picture in the MPEG system, already decoded I picture or P picture data is read out from frame memory 16, and is then delivered to motion compensating circuit 15. The data delivered to the motion compensating circuit 15 is caused to undergo motion compensation thereat, and is then delivered to adding circuit 14. Since the adding circuit 14 adds data outputted from inverse DCT circuit 18 and data outputted from motion compensating circuit 15, decoded B picture data will be obtained. This data is also stored into frame memory 16.
Picture data decoded and stored into the frame memory 16 in this way are caused to undergo D/A conversion at D/A converter 17. Thereafter, such picture data are delivered to display 18, and are displayed thereon.
Meanwhile, as described above, control circuit 31 delivers, in correspondence with code request signal from video code buffer memory 10, data stored in ring buffer memory 5 to video code buffer memory 10. In this case, when, e.g., data processing relating to simple picture are continued and data transfer quantity from video code buffer memory 10 to inverse VLC circuit 11 is thus decreased, data transfer quantity from ring buffer memory 5 to video code buffer memory 10 is also decreased. Consequently, memory data quantity of ring buffer memory 5 is increased, resulting in the possibility that it may overflow.
For this reason, track jump judging circuit 7 calculates, from write point (WP) and reproduction point (RP) subject to control by control circuit 31, data quantity that ring buffer memory 5 currently stores, whereby in the case where that data quantity exceeds a predetermined reference value set in advance, it judges that ring buffer memory 5 may overflow to output track jump command to tracking servo circuit 8.
Moreover, the track jump judging circuit 7 is operative so that in the case where it detects sector No. abnormal condition signal from sector detecting circuit 4 or error generation signal from ECC circuit 6, it determines (calculates), from write point (WP) and reproduction point (RP) subject to control by control circuit 31, data quantity remaining within ring buffer memory 5. In addition, the track jump judging circuit 7 determines (calculates), from current track position, data quantity to allow ring buffer memory 5 not to underflow, which is required for guaranteeing read-out from ring buffer memory 5 to video code buffer memory 10.
In the case where remaining data quantity of ring buffer memory 5 is sufficiently large, even if data is read out from ring buffer memory 5 to video code buffer memory 10 at the maximum transfer rate, no underflow takes place in the ring buffer memory 5. For this reason, track jump judging circuit 7 reproduces, for a second time, error occurrence position by means of pick-up 2 to thereby judges that error recovery can be made to output track jump command to tracking servo circuit 8.
When track jump command is outputted by track jump judging circuit 7, tracking servo circuit 8 allows reproduction position by pick-up 2 to be subjected to track jump. Namely, in the case where data are recorded, e.g., from the inner circumference to the outer circumference of optical disc 1, tracking servo circuit 8 jumps pick-up 2 from current position to the adjacent track on the inner circumferential side. Then, for a time period during which reproduction position by pick-up 2 arrives at the original position as the result of the fact that optical disc 1 makes one rotation for a second time, i.e., for a time period until sector No. obtained from sector detecting circuit 4 becomes equal to sector No. at the time of track jump, writing into ring buffer memory 5 of new data is inhibited, and data already stored in the ring buffer memory 5 is transferred, as occasion demands, to video code buffer memory 10.
Moreover, even if sector No. obtained from sector detecting circuit 4 is in correspondence with sector No. at the time of track jump after track jump, in the case where quantity of data stored in ring buffer memory 5 is above a predetermined reference value, i.e., in the case where ring buffer memory 5 may overflow, writing of data into ring buffer memory 5 is not restarted, and track jump is carried out for a second time.
In this example, ring buffer memory 5 has a capacity capable of storing data of at least one track of optical disc 1.
Thus, in the case where optical disc 1 is, e.g., CLV (Constant Linear Velocity) disc, since rotation period is maximum at the outermost circumference, this optical disc 1 at least has a memory capacity corresponding to one track at the outermost circumference, i.e., memory capacity of (rotation period of the outermost circumference).times.(data transfer rate from ECC circuit 6 to ring buffer memory 5).
Maximum transfer rate of data from ring buffer memory 5 to video code buffer memory 10 is set to a value equal to data transfer rate from ECC circuit 6 to ring buffer memory 5, or a value smaller than that value. By making such a setting, it is possible to freely send out code request of data transfer from video code buffer memory 10 to ring buffer memory 5 irrespective of timing of track jump.
As stated above, in accordance with the above-mentioned optical disc apparatus, since pick-up 2 is caused to undergo track jump in correspondence with memory capacity of ring buffer memory 5, overflow or underflow of video code buffer memory 10 is prevented irrespective of complexity or flatness of reproduction picture from optical disc 1. Thus, it is possible to reproduce picture of uniform picture quality for a long time.
Further, in accordance with the above-mentioned optical disc apparatus, in the case where any error takes place in data which has been read out from optical disc 1, since an approach is employed to allow pick-up 2 to undergo track jump to read out data from optical disc 1 for a second time, it is possible to prevent deterioration of reproduction picture by read-out error of data.
Meanwhile, ECC circuit 6 in the optical disc apparatus of FIG. 1 is constituted as shown in FIG. 2, for example. Data outputted from the above-described demodulating circuit 3 shown in FIG. 1 is inputted to ECC circuit 6 through sector detecting circuit 4, and is temporarily stored into buffer memory 41 of the input stage thereof. The data stored in the buffer memory 41 are sequentially transferred to memory 42 and are stored thereinto in accordance with address that address generator 43 generates. The data stored in the memory 42 are read out therefrom and are transferred to error correcting circuit 44. This error correcting circuit 44 implements error correction to the data transferred from the memory 42 to store the error-corrected data into the memory 42 for a second time.
Write and read operations of data with respect to memory 42 will now be described with reference to the memory map of FIG. 3. Circular mark in the figure indicates one symbol unit of error correction, ordinarily 1 byte. Write or read operation of data with respect to memory 42 is carried out in units where one row (line) in lateral direction of the memory map shown in FIG. 3 is caused to be one (unit) data length. Moreover, parity bits are added to the last portion to which slanting lines are attached in the figure, and respective parity bits as data of the last portion in arrangement of data in oblique direction (hereinafter described as "interleaving direction") of the memory map indicated by arrow of dotted line in the figure serves as parity bit for correcting error of the data arranged in the interleaving direction.
Namely, in order to allow, e.g., burst error to be isolated, data and parity bits for correcting error of that data are arranged in the interleaving direction.
Accordingly, in the memory 42, data from buffer memory 41 is first written in the address direction in accordance with address that write pointer wp1 points (indicates).
In this example, the address direction means a direction in which address is advanced from the left to the right and from the top to the bottom in the memory map of FIG. 3.
Data already written in memory 42 is read out in the interleaving direction at least in accordance with address that read pointer rp1, which is delayed by memory capacity necessary for reading out data in the interleaving direction (hereinafter described as interleaving length) points (indicates), and is delivered to error correcting circuit 44. At this error correcting circuit 44, error correction processing is implemented to arrangement of data in the interleaving direction in a manner as described above. Thus, the error corrected data is transferred to memory 42.
The data which has been error-corrected in the error correcting circuit 44 is written for a second time at address position initially written in accordance with address that write pointer wp2 points (indicates), and is transferred to buffer memory 45 in accordance with read pointer rp2 moving in the address direction.
The above-mentioned operation is caused to be one cycle to repeat such a cycle so that error-corrected data are sequentially outputted from buffer memory 45 to ring buffer memory 5.
Accordingly, error-corrected data is once (temporarily) stored into memory 42 and is stored into ring buffer memory 5 for a second time.
As stated above, in the conventional optical disc apparatus, there is carried out a redundant operation such that data are sequentially outputted from different two memories, i.e., memory 42 and ring buffer memory 5 and are inputted thereto. As a result, there were the problems that not only scale of the apparatus becomes large, but also data processing speed becomes lower.
In view of the above, the applicant of this application has already proposed, in EUROPEAN PATENT APPLICATION Publication number 0 590 881 A2 (Date of publication: 06 April 1994 Bulletin 94/14), a system for correcting error of data stored in the ring buffer memory 5.
However, in the above-mentioned proposed system, correct sector address could not be read, thus disadvantageously failing to precisely and quickly provide an access to optical disc 1.
Further, there was the problem that in the case where correction is impossible because there is great error in data which has been read from optical disc 1, it is impossible to make correction for a second time.
In addition, there was the problem that it takes much time in de-interleaving operation, so high speed reproducing operation is difficult at the time of special reproduction, such as, for example, fast feed or rewinding.
This invention has been made in view of such circumstances, and contemplates providing an ability to quickly make an access to the disc, and providing an ability to reproduce the disc at a higher speed.
In addition, this invention contemplates improving error correcting ability.